For the production of plastic products by molding, there is conventionally used a molding apparatus containing two metal molds, i.e., a male mold and a female mold facing each other, between which plastic materials are poured to form a plastic product having a desired shape. In the conventionally used apparatus for molding, since two metal molds are always required, the production of the male and female molds having complex shapes is troublesome and requires skilled technique and a long time for production, which results in high expense. Meanwhile, also in case of the production of molded products using metal plates, male and female molds are conventionally required. For the production of molded products using metal plates, a metal plate having a desired shape is previously struck, and the struck metal plate is placed between male and female molds, to which a pressure is applied to give a molded product. In this case, depending on the desired shape of the curve, the molding is required to be effected for a plurality of times for the purpose of prevention of breakage of the materials and production of creases thereon. For the respective production steps, plural pairs of the combined molds having different sizes are required, thus resulting in a great expense in the production of the molds. Further, in the conventional production of metal plate-made products, finishing treatments such as polishing, plating, coating, etc. are required, and thereby, the number of production steps increases, which is economically disadvantageous.
Further explanation is given of the conventional production of a molded product having curved shape, with reference to the accompanying drawings. In the production of molded products having a curved shape such as a mudguard for bicycles, etc. using plastic, as shown in FIGS. 1 and 2, a male mold 1a and a female mold 5a are opposed to each other to form a space between them. Into the space a plastic material in a liquid state is poured through a hole 18 with the application of high pressure to form a product having a sectional shape a.sub.1. In this case, the joint between the male mold 1a and the female mold 5a excluding the hole 5a.sub.1 is required to be air-tight. When the joint contains any gaps, the poured material leaks out from the gaps, and as a result a product of inferior quality is obtained. For preventing this, the portions forming the joint are required to be formed with high precision. In addition, the thickness of the product also depends on the precision of forming of the male and female molds. Thus, the precision of forming of the male and female molds determines the quality of the products, the production of the molds requires skilled technique and considerable expenses.
For the production of a molded product having curved shape using a metal plate, as shown in FIG. 3, a plate material c is inserted between a male mold 5b and a female mold 1b which constitute a metal mold for pressing, and the inserted material is struck by the action of the male mold 5b being inserted into the female mold 1b to give a metal plate c.sub.1 having the desired shape. Then, the obtained metal plate c.sub.1 is put into other molds having curved shapes, i.e. a male mold 5c and a female mold 1c, as shown in FIGS. 5 and 6, and pressed to produce a metal product c.sub.2. In the press-molding as above described, however, when a product having a curved shape is produced, the starting material undergoes much distortion, and as a result, when the precision of the shape of the male mold 5c and the female mold 1c are inferior, many creases are produced in the product or the periphery of the product becomes irregular so that in many cases finishing treatments are needed. Further, in the press-molding, when the metal product c.sub.2 having a largely curved shape is desired, as shown in FIG. 5, the pressing processes are effected in a series of steps so as to gradually press the material. If the pressing is effected once and radically, the elongation of the material does not follow the pressing force so that the material is cracked. As the result, the production of the molds is disadvantageously expensive.
As described above, in the production of various molded products of plastics or metal plates by using the conventional means for molding, the male and female molds are always required. The present invention provides a molding apparatus comprising one main molding roll. In the molding apparatus of the present invention, softened plastic materials which are in the shape of belts or rods are introduced onto the peripheral surface of the main molding roll, and thereby a plastic product having a shape according to that of the main molding roll can easily be obtained.